Thermoplastic resins are used typically for the production of products such as extruded films, sheets, profiles, post-formed moldings, composite structures, and laminates. For maintaining the beauty of such thermoplastic resin products over the long term, tough and transparent hard coatings, which are resistant to scratches and abrasion, are generally applied as a surface-protecting layer. Such hard coatings generally also exhibit satisfactory surface-protecting functions typically against outdoor exposure or chemical substances such as solvents and detergents.
Multifunctional (meth)acrylate oligomers or monomers are used as regular hard coatings to be applied to thermoplastic resin products. These multifunctional (meth)acrylate oligomers or monomers are cured by the action of active energy rays and thereby give hard coatings which exhibit satisfactory scratch resistance, abrasion resistance, hardness, and chemical resistance.
The resulting hard coatings obtained from multifunctional (meth)acrylate oligomers or monomers by curing with active energy rays are resistant to scratches and abrasion to some extent, but may often suffer from cracking and failure (breakage) of the entire thermoplastic resin products upon receiving of impact. These coatings, when exposed to outdoors over the long term, may suffer from cracking or chalking. As a possible solution to this problem, there is a technique of imparting flexibility to a hard coating by the combination use of a (meth)acrylate oligomer or monomer being monofunctional or having a large double bond equivalent (PTL 1, PTL 2, and PTL 3). However, it is very difficult for this technique to provide properties required of a hard coating, i.e., rigidity (hardness), flexibility to endure impact, and weather resistance to endure long-term outdoor exposure all at satisfactory levels, because the resulting hard coating has a remarkably decreased hardness to thereby deteriorate in scratch resistance and abrasion resistance, although having better impact resistance. In other words, these properties are trade-off properties for the hard coatings.
As a possible solution to provide scratch/abrasion resistance and impact resistance both at satisfactory levels, there is proposed an active energy ray curable coating composition including silica microparticles in combination with a urethane acrylate using a polyalkylene glycol derivative (PTL 4).